Superior Energy Storage Properties and Optical Transparency in K 0.5 Na 0.5 NbO 3 -Based Dielectric Ceramics via Multiple Synergistic Strategies.

Eco-friendly transparent dielectric ceramics with superior energy storage properties are highly desirable in various transparent energy-storage electronic devices, ranging from advanced transparent pulse capacitors to electro-optical multifunctional devices. However, the collaborative improvement of energy storage properties and optical transparency in KNN-based ceramics still remains challenging. To address this issue, multiple synergistic strategies are proposed, such as refining the grain size, introducing polar nanoregions, and inducing a high-symmetry phase structure. Accordingly, outstanding energy storage density (W total  ≈7.5 J cm -3 , W rec  ≈5.3 J cm -3 ) and optical transmittance (≈76% at 1600 nm, ≈62% at 780 nm) are simultaneously realized in the 0.94(K 0.5 Na 0.5 )NbO 3 -0.06Sr 0.7 La 0.2 ZrO 3 ceramic, together with satisfactory charge-discharge performances (discharge energy density: ≈2.7 J cm -3 , power density: ≈243 MW cm -3 , discharge rate: ≈76 ns), surpassing previously reported KNN-based transparent ceramics. Piezoresponse force microscopy and transmission electron microscopy revealed that this excellent performance can be attributed to the nanoscale domain and submicron-scale grain size. The significant improvement in the optical transparency and energy storage properties of the materials resulted in the widening of the application prospects of the materials.